Hybrid Electric Aircraft Research Articles

Conceptual Design and Energy Storage Positioning Aspects for a Hybrid-Electric Light Aircraft

Abstract This work is a feasibility study of a 19-passenger hybrid-electric aircraft, to serve the short-haul segment within the 200–600 nautical miles. Its ambition is to answer some dominating research questions, during the evaluation and design of aircraft based on alternative propulsion architectures. The potential entry into service (EIS) is foreseen beyond 2030. A literature review is performed to identify similar concepts under research and development. After the requirements' definition, the first level of conceptual design is employed. The objective of design selections is driven by the need to reduce CO2 emissions and accommodate aircraft electrification with boundary layer ingestion engines. Based on a set of assumptions, a methodology for the sizing of the hybrid-electric aircraft is described to explore the basis of the design space, incorporating a parametric analysis for the consideration of boundary layer ingestion effects. Additionally, a methodology for the energy storage positioning is provided to highlight the multidisciplinary aspects between the sizing of an aircraft, the selected architecture (series/parallel partial hybrid), and the storage characteristics. The results show that it is not possible to fulfill the initial design requirements (600 nmi) with a fully-electric aircraft configuration, due to the far-fetched battery necessities. It is also highlighted that compliance with airworthiness standards is favored by switching to hybrid-electric aircraft configurations and relaxing the design requirements (targeted range, payload, battery technology). Finally, the lower degree of hybridization (40%) is observed to have a higher energy efficiency (−12% energy consumption) compared to the higher degree of hybridization (50%) and greater CO2 reduction, with respect to the conventional configuration.

Innovative Management of Design Concepts Research and International Cooperation on EU Programs for creating Hybrid Electric Aircraft & Airship

Fast and expanded implementation of the most relevant innovative developments is becoming a fundamental trend in the strategy of breakthrough economic development of advanced countries. However, today finding and implementing any original idea or a new scientific discovery or technological solution requires more and more tool costs. It is necessary to use highly valuable experience of smart specialists and provide considerable financial support for foreign economic cooperation and targeted scientific interaction on an international level. MAI was included in two international consortiums for the new European programs INEA 2020-2023 to create new promising environmental models of Hybrid Electric Propulsion systems for FUTPRINT50 and IMOTHEP regional passenger aircraft projects.

Community Noise Assessment of Hybrid-Electric Aircraft Using Windmilling Drag on Approach

The modeling and assessment of the community noise impacts of a representative hybrid-electric aircraft implementing windmilling motors as drag generators on approach is presented. An increasing desire to reduce emissions caused by aviation has motivated the development of hybrid-electric aircraft that have some degree of their traditional gas-turbine propulsion replaced with electric propulsion. Turboelectric propulsion offers flexibility in the engine architecture that allows hybrid-electric aircraft to be capable of certain advanced operational noise abatement flight procedures. Steep and delayed-configuration approaches are example flight procedures that enable significant noise reductions on approach but require the aircraft to have enough drag for the approach to be stable. Windmilling is an alternative mechanism to create drag during descent and is possible in architectures where the fan is powered by an electric motor. Results examining the potential benefits of representative turboelectric aircraft implementing this controlled drag concept on both delayed deceleration and steeper approaches are presented. The results indicate that windmilling fans are quieter than standard drag-producing devices and can be used to yield significant community noise reductions compared to aircraft performing standard 3 deg continuous descent approaches.

Computational modeling of a lithium‐ion battery thermal management system with Al 2 O 3 ‐based nanofluids

Lithium-ion batteries are seen as the primary energy storage tools for hybrid electric aircraft. However, the high temperature that occurs in battery modules can lead to a reduction in the capacity of the batteries and may even lead to serious safety issues such as fire. Therefore, it is essential to design an effective and reliable thermal management system to maintain battery temperatures under acceptable thresholds. In this study, a battery management system was designed using Al2O3 nanofluid in different configurations, incorporating two different cooling models based on longitudinal and transverse flow directions, where the battery module consisted of 20 prismatic lithium-ion batteries. The two models were compared in terms of discharge rates, volume fraction values of nanofluid, and inlet velocities, and temperatures of the coolant. Overall, it was evident that the battery module was within the safe temperature range when cooled with the nanofluid, but not air. Novelty Statement Lithium-ion batteries are seen as primary energy storage tools for hybrid electric aircraft. Thermal analysis of the batteries was performed in three dimensions by taking the bus bars into consideration. Nano fluid cooling was used as an effective way to keep battery temperatures within acceptable ranges.

4-MW Class High-Power-Density Generator for Future Hybrid-Electric Aircraft

This article describes the underpinning research, development, construction, and testing of a 4-MW multithree phase generator designed for a hybrid-electric aircraft propulsion system demonstrator. The aim of the work is to demonstrate gravimetric power densities around 20 kW/kg, as required for multi-MW aircraft propulsion systems. The key design choices, development procedures, and tradeoffs, together with the experimental testing of this electrical machine connected to an active rectifier, are presented. A time-efficient analytical approach to the downselection of various machine configurations, geometrical variables, different active and passive materials, and different thermal management options is first presented. A detailed design approach based on the 3-D finite element analysis (FEA) is then presented for the final design. Reduced power tests are carried out on a full-scale 4-MW machine prototype, validating the proposed design. The experimental results are in good agreement with simulation and show significant progress in the field of high-power-density electrical machines at the targeted power rating.

Optimal Sizing and Operation of Airport Infrastructures in Support of Electric-Powered Aviation

The adoption of hybrid-electric aircraft is expected to have a considerable impact on airport operations, with the need of new infrastructural requirements to support electric-powered fleets. In particular, battery-charging requirements shall play a decisive role. Preliminary investigations useful to perform scenario studies for the future implementation of electric-powered aviation can take advantage of the ARES methodology presented here, which provides the optimal solution to the sizing of airport battery recharging infrastructures. Based on the flight schedule and on the specifications of the aircraft fleet and the charging equipment, the solution assesses the number and type of charging points, the related electrical consumption in terms of energy and power, and further information needed to guarantee the required operational level while minimizing the procurement and operating costs. The method allows considering and comparing two charging strategies: plug-in recharge and battery swapping. Energy price variation in time is also taken into account and a full description of the optimal time scheduling of recharging operations is provided. Application studies to the reconfiguration of two existing aerodromes, a General Aviation airport and a large regional hub, are discussed, showing the potential of the proposed approach.

Thermal management system with nanofluids for hybrid electric aircraft battery

Electric aircraft should be used more intensively due to the increase in energy consumption and the decrease in reserves of fossil fuels. Batteries are also an important factor in the development of electric aircraft. One of the most important parameters for the effective operation of batteries is the evaluation of heat dissipation. The even distribution or reduction of the heat generated during the operation of lithium-ion batteries extends the life of the batteries and ensures the safety of electric aircraft. In order to improve heat transfer dissipation in batteries in hybrid electric aircraft, it is necessary to increase the thermal conductivity of the coolant. For this reason, it has been suggested that solid particles with high thermal conductivity should be added to the coolant. In the present study, different battery thermal management strategies are suggested. To research the effect of nanofluids for thermal management in lithium-ion batteries, the study included two different base fluids (water and ethylene glycol) and three different volumetric fractions (1%, 2%, and 5%) of nanoparticle (Fe2O3) were added to these fluids. While the study was evaluated at four different discharge rates (1.0, 1.5, 2.0, and 2.5), the inlet velocities and temperature of the fluid were also changed. The cooling performances for 15 batteries module were examined and the simulation results showed that the nanofluid-based coolant could keep the temperature of the module at the desired value. As a result of the analysis, water was found to be the best nanofluid coolant parameter because it had a higher thermal conductivity than ethylene glycol. When the C value of the battery module was increased, that is, when the module was charged faster, its temperature increased. It was seen that the module was cooled better when the volume fraction of nanofluids and the speed of the refrigerant were increased.

Thermal Management challenges for HEA – FUTPRINT 50

Electric and Hybrid-Electric Aircraft (HEA) incorporate new systems, which demand an integration level higher than classical propulsion architectures systems do. High power electrical motors, converters, batteries or fuel cells, and distributed propulsion, all introduce new kinds of heat sources and dynamics that have to be accounted for and regulated. The latent opportunity to explore synergies among these systems requires the development of new models and their coupling with multi-disciplinary design optimization (MDO) toolchains. Also, an understanding of the implications into aircraft operations and trade-offs are critical to evaluate and validate gains at the aircraft level. This paper provides a definition of thermal management and functions of thermal management system (TMS) in aircraft, HEA thermal management challenges, main opportunities, conclusions and the way forward. A discussion of road ahead, regarding development of capabilities to support the design of TMS will be brought to the fore along the project, showcasing the open approach of FUTPRINT50 to be driven by open collaboration in order to accelerate the entry into service of this type of aircraft.

Selecting figures of merit for a hybrid-electric 50-seat regional aircraft

In the course of the aircraft design process for a hybrid-electric aircraft, a number of configuration alternatives have to be assessed. In addition, novel propulsion concepts have to be compared to a conventional reference aircraft. These comparisons are carried out by means of suitable figures of merit, adapted to a reference mission. This work will give insight into the process of identifying suitable figures of merit for a 50-seat hybrid-electric regional aircraft, which was carried out in the Horizon 2020 project FutPrInt50. Coming from a thorough perspective, a down-selection leads to a graspable number of parameters which are categorized in regard to the environment, to the airline desirability, and to the introduction of hybrid-electric aircraft. Those figures of merit, like emissions and operating costs, are gathered in an objective function which can support an overall evaluation of the aircraft design. This offers a detailed, yet transparent assessment of the various designs.

Hybrid electric distributed propulsion overall aircraft design process and models for general aviation (FAST GA)

In the frame of the European objectives in terms of CO2 emissions, the aeronautics is looking for a technological rupture to achieve them, in particular, the aircraft design domain pursuits this through the research of innovative architectures. One of these innovative configurations currently being explored includes the hybrid electric energy source (thermal/electric) for Distributed Electric Propulsion (DEP) architecture. This Paper details a code developed to size a general aviation aircraft at concept level, by only defining its top level requirements and the main architecture parameters. The code can manage both conventional and hybrid power source as well as concentred or distributed propulsion architectures in order to allow the user to evaluate and compare the feasibility and benefits respectively of these innovative architectures. This code is a branch of the code “FAST-CS25” (Future Aircraft Sizing Tool for conventional CS-25 type) held by ONERA/ISAE-SUPAERO. The presented work aims at the expansion of the FAST code to CS-23 conventional type, hybrid electric energy source, and distributed propulsion system configurations. Through this paper, the models and the main sizing loops for the concept design are described, but putting special emphasis on the distributed propulsion aerodynamics and wing mass estimation. These detailed models where validated with the NASA X-57 DEP aircraft satisfactory. The whole concept design loop of a hybrid energy aircraft was validated with the eGenius hybrid energy aircraft.

Innovation design analysis of the optimal aerodynamic adaptive smart structures for disk-body solar Hybrid Electric aircraft and airship concepts

The innovation integrated design analysis of the concept of finding any optimal aerodynamic structure with adaptive intelligent systems as a means of changing facility of the geometric shape of the surface by integrating the disc wing-body of a solar Hybrid Electrical aircraft (HEA) and an airship to reduce weight, power and fuel sources is very relevant today and focused on the international research EC programs of future green ecology air transportation. The universal digital method for optimizing the CAD aircraft design is presented which is focused on achieving the goal of minimum weight-drag-frontal stability of the layout from the virtual center of mass allows us to get the layout of the aircraft from the conditions of reducing the time of full flight operation of E-Mobility and low cost for priority with realize a short take-off and landing (STOL) with high angle of the flight path and compact infrastructural restrictions in the terminal slot configurations of modern urban airport infrastructure and achieving zero toxic & noise regulation by IATA/ICAO. The joint results of EC international R&D collaboration to accelerate the synergy effect of new aircraft concepts.

THEA-CODE: a design tool for the conceptual design of hybrid-electric aircraft with conventional or unconventional airframe configurations

The aviation world is dealing with the development of new and greener aviation. The need for reducing greenhouse gas emission as well as the noise is a critical requirement for the aviation of the future. The aviation world is struggling with it, and a compelling alternative can be the electric propulsion. This work aims to present THEA-CODE, a tool for the conceptual design of hybrid-electric aircraft. The tool evaluates the potential benefits of the electric propulsion in terms of fuel burnt and direct and indirect CO2emissions. THEA-CODE is suitable not only for conventional “wing-tube” configurations but also for unconventional ones, such as the box-wing. The results show a significant reduction of fuel burnt adopting batteries with energy density higher than the current state of the art. A procedure to find the potential best compromise configurations is presented as well.

Failure Modes and Reliability Oriented System Design for Aerospace Power Electronic Converters

Aircraft electrification has been a major trend in aviation industry for past 20 years. Given the increasing electrical power requirement for future more electric aircraft and hybrid electric aircraft, research efforts has been ongoing in high power electrical conversion for air-borne systems. Safety critical nature of aviation systems places reliability of aerospace power converters as a critical design concern. In this paper, power electronic system reliability is studied with emphasis on lifetime limiting factors of critical sub components. Reliability of voltage source power converters at different system voltage levels are modelled for a starter generator drive converter. A key observation is that Si IGBT devices are sufficient with respect to reliability requirements in low and medium voltage systems (up to 540 V). At higher system voltages (above 540 V), multi level topologies are necessary for designing with Si IGBTs. In constant power profile drive, system reliability is minimally affected by wear-out failure of film capacitors in converter DC links. In multi level topologies without enhanced voltage derating, system reliability is dominated by cosmic ray induced random failures. Simulation results demonstrate that at high system voltages (810 V), 2 L topology with SiC mosfets outperform Si IGBT based 3 L topology with respect to reliability.

Design and Optimization of Ram Air–Based Thermal Management Systems for Hybrid-Electric Aircraft

Ram air–based thermal management systems (TMS) are investigated herein for the cooling of future hybrid-electric aircraft. The developed TMS model consists of all components required to estimate the impacts of mass, drag, and fuel burn on the aircraft, including heat exchangers, coldplates, ducts, pumps, and fans. To gain a better understanding of the TMS, one- and multi-dimensional system sensitivity analyses were conducted. The observations were used to aid with the numerical optimization of a ram air–based TMS towards the minimum fuel burn of a 180-passenger short-range partial-turboelectric aircraft with a power split of up to 30% electric power. The TMS was designed for the conditions at the top of the climb. For an aircraft with the maximum power split, the additional fuel burn caused by the TMS is 0.19%. Conditions occurring at a hot-day takeoff represent the most challenging off-design conditions for TMS. Steady-state cooling of all electric components with the designed TMS is possible during a hot-day takeoff if a small puller fan is utilized. Omitting the puller fan and instead oversizing the TMS is an alternative, but the fuel burn increase on aircraft level grows to 0.29%.

Impact of Hybrid-Electric Aircraft on Contrail Coverage

Aviation is responsible for approximately 5% of global warming and is expected to increase substantially in the future. Given the continuing expansion of air traffic, mitigation of aviation’s climate impact becomes challenging but imperative. Among various mitigation options, hybrid-electric aircraft (HEA) have drawn intensive attention due to their considerable potential in reducing greenhouse gas emissions (e.g., CO2). However, the non-CO2 effects (especially contrails) of HEA on climate change are more challenging to assess. As the first step to understanding the climate impact of HEA, this research investigates the effects on the formation of persistent contrails when flying with HEA. The simulation is performed using an Earth System Model (EMAC) coupled with a submodel (CONTRAIL), where the contrail formation criterion, the Schmidt–Appleman criterion (SAC), is adapted to globally estimate changes in the potential contrail coverage (PCC). We compared the HEA to conventional (reference) aircraft with the same characteristics, except for the propulsion system. The analysis showed that the temperature threshold of contrail formation for HEA is lower; therefore, conventional reference aircraft can form contrails at lower flight altitudes, whereas the HEA does not. For a given flight altitude, with a small fraction of electric power in use (less than 30%), the potential contrail coverage remained nearly unchanged. As the electric power fraction increased, the reduction in contrail formation was mainly observed in the mid-latitudes (30° N and 40° S) or tropical regions and was very much localized with a maximum value of about 40% locally. The analysis of seasonal effects showed that in non-summer, the reduction in contrail formation using electric power was more pronounced at lower flight altitudes, whereas in summer the changes in PCC were nearly constant with respect to altitude.

First-Fault Detection in DC Distribution With IT Grounding Based on Sliding Discrete Fourier-Transform

Since dc distribution minimizes the number of power conversion stages, it lowers the overall cost, power losses, and weight of a power system. Critical systems use IT grounding because it is tolerant to the first-fault. Hence, this is an attractive option for hybrid electric aircraft (HEA), which combines gas engines with electric motors driven by power electronic converters. This letter proposes an accurate implementation for the procedure of first-fault detection with IT grounding. The ac component injection along with the sliding discrete Fourier transform (SDFT) is used to estimate the fault impedance. The procedure is very accurate due to the heavy filtering of the implicit moving average filter. Further computation savings are obtained by using the double look-up tables, and the Goertzel algorithm for the SDFT. Results are validated by simulations and experiments.

Tomorrow Man

Jean Botti, CEO of VoltAero discusses the development progress of the Cassio hybrid-electric aircraft and the journey to more sustainable aviation

Thermal and Electrical Performance in High-Voltage Power Modules With Nonmetallic Additively Manufactured Impingement Coolers

As high voltage, wide-band-gap power modules increase in power density with high switching frequency, they create localized hot spots and harmful electromagnetic interference (EMI). If not treated properly, these issues can drastically reduce the reliability of the devices. In this article, we propose a solution to address both of these challenges created by power module building blocks which are designed for use in a hybrid-electric aircraft traction inverter. Additive manufacturing is used to fabricate a nonmetallic jet impingement device to decrease power module temperatures. Moreover, the nonmetallic structure limits the accentuation of EMI created by the module operating at high switching frequencies. Conjugate heat transfer simulations are used to predict the thermal performance of the cooler. In this article, a reduction of maximum die temperatures is observed, along with an increase in temperature uniformity throughout the base plate. Experimental results show a minimum thermal resistance of 0.1 K/W and an average heat transfer coefficient up to 3600 W/m2.K at peak operation. Finally, EMI tests are performed to show a two orders of magnitude reduction of parasitic capacitance using the nonmetallic cooler compared with a metallic heat sink. This directly leads to a 25 dB decrease in the common mode noise.

Sustainability Assessment and Engineering of Emerging Aircraft Technologies—Challenges, Methods and Tools

Driven by concerns regarding the sustainability of aviation and the continued growth of air traffic, increasing interest is given to emerging aircraft technologies. Although new technologies, such as battery-electric propulsion systems, have the potential to minimise in-flight emissions and noise, environmental burdens are possibly shifted to other stages of the aircraft’s life cycle, and new socio-economic challenges may arise. Therefore, a life-cycle-oriented sustainability assessment is required to identify these hotspots and problem shifts and to derive recommendations for action for aircraft development at an early stage. This paper proposes a framework for the modelling and assessment of future aircraft technologies and provides an overview of the challenges and available methods and tools in this field. A structured search and screening process is used to determine which aspects of the proposed framework are already addressed in the scientific literature and in which areas research is still needed. For this purpose, a total of 66 related articles are identified and systematically analysed. Firstly, an overview of statistics of papers dealing with life-cycle-oriented analysis of conventional and emerging aircraft propulsion systems is given, classifying them according to the technologies considered, the sustainability dimensions and indicators investigated, and the assessment methods applied. Secondly, a detailed analysis of the articles is conducted to derive answers to the defined research questions. It illustrates that the assessment of environmental aspects of alternative fuels is a dominating research theme, while novel approaches that integrate socio-economic aspects and broaden the scope to battery-powered, fuel-cell-based, or hybrid-electric aircraft are emerging. It also provides insights by what extent future aviation technologies can contribute to more sustainable and energy-efficient aviation. The findings underline the need to harmonise existing methods into an integrated modelling and assessment approach that considers the specifics of upcoming technological developments in aviation.

Multidisciplinary Design Optimization Framework with Coupled Derivative Computation for Hybrid Aircraft

Hybrid-electric aircraft are a potential way to reduce the environmental footprint of aviation. Research aimed at this subject has been pursued over the last decade; nevertheless, at this stage, a full overall aircraft design procedure is still an open issue. This work proposes to enrich the procedure for the conceptual design of hybrid aircraft found in literature through the definition of a multidisciplinary design optimization (MDO) framework aimed at handling design problems for such kinds of aircraft. The MDO technique has been chosen because the hybrid aircraft design problem shows more interaction between disciplines than a conventional configuration, and the classical approach based on multidisciplinary design analysis may neglect relevant features. The procedure has been tested on the case study of a single-aisle aircraft featuring hybrid propulsion with distributed electric ducted fans. The analysis considers three configurations (with 16, 32, and 48 electric motors) compared with a conventional baseline at the same 2035 technological horizon. To demonstrate the framework’s capability, these configurations are optimized with respect to fuel and energy consumption. It is shown that the hybrid-electric concept consumes less fuel/energy when it flies on short range due to the partial mission electrification. When one increases the design range, penalties in weight introduced by hybrid propulsion overcome the advantages of electrified mission segment: the range for which hybrid aircraft have the same performance of the reference conventional aircraft is named the “breakdown range.” Starting from this range, the concept is no longer advantageous compared to conventional aircraft. Furthermore, a tradeoff between aerodynamic and propulsive efficiency is detected, and the optimal configuration is the one that balances these two effects. Finally, multiobjective optimization is performed to establish a tradeoff between airframe weight and energy consumption.